1. Field of the Invention
The present invention relates to the selective chlorination of phenolic compounds, in the ortho position relative to the hydroxyl group, using gaseous chlorine.
2. Description of the Prior Art
In the preparation of chlorophenols by chlorination of phenol, isomers are obtained at the various reaction stages, and this ultimately gives rise to numerous compounds which must subsequently be separated by means of costly and difficult purification techniques. On the other hand, the ratios of the various isomers obtained do not automatically correspond to that which would be economically worthwhile, given the existing markets.
Need therefore exists for processes enabling a selective chlorination, especially for a selective chlorination in the ortho position or in the para position relative to the hydroxyl group of the phenolic compound.
Thus, published German Patent Application No. 3,318,791 describes a process for the selective chlorination of phenol to give 2-chlorophenol, in a perchlorinated apolar solvent and in the presence of a branched-chain amine.
However, the use of a solvent in an industrial scale chlorination process may, in certain cases, present disadvantages, such as, for example, the requirement for a larger reactor volume and a more difficult separation of the reaction products.
Cf. U.S. Pat. No. 4,160,114, Patent Abstracts of Japan, 11, No. 43 (C-402) [2490], Feb. 7, 1987, and JP-A-61/207,351.